1. Field of the Invention
The present invention relates generally to wireless networks and communication systems. More particularly, the preferred embodiments of the present invention relate to methods and systems for providing intelligent repeaters in spread spectrum communication systems to support selective amplification of communication channels and signals therein.
2. Description of the Related Art
The field of spread spectrum, wireless communication has been active for over a decade. For instance, the advantages of an exemplary code division multiple access (CDMA) system are described in U.S. Pat. No. 4,901,307 issued Feb. 13, 1990 to K. Gilhousen et al. While many factors dictate the capacity of a spread-spectrum wireless network, received signal power and noise power at the network nodes are important factors in considering network capacity. Most conventional strategies for increasing network capacity may be viewed as a means: 1) to increase signal power; 2) to decrease interference; or 3) to instill tolerance for lower signal to interference plus noise ratios (SINR). In this context, to extend network coverage in rural areas or into obstructed or shadowed areas, conventional repeaters have classically been used as a means to increase received signal power and reduce transmitted power requirements for originating nodes. As understood in the art, repeaters are devices that amplify or regenerate signals in order to extend the transmission distance. As network usage continues to grow, however, particularly in dense urban subscriber areas, excessive multiple access interference (MAI) is becoming a primary limitation to network capacity. This network state is known as reaching pole capacity. Conventional repeaters amplify all received signals and, as such, do little to improve the signal to interference power ratio. Consequently, conventional repeaters are generally ineffective for increasing the pole capacity. As understood in the art, MAI is a significant noise source limiting the practical capacity and performance of second generation, spread-spectrum based wireless services, such as one based on CDMA digital transmission. A number of techniques employing the aforementioned strategies for increasing network capacity have been proposed for compensating the MAI associated with spread spectrum wireless systems.
The foremost conventional technique for compensating MAI and ensuring reliable communication is to control the transmitted power from both the mobile station and the base station (BS). Several examples of this technique are described in U.S. Pat. Nos. 6,119,010, 6,118,983, and 6,104,933. A second technique relies on controlling the patterns of the receiving and transmitting antennas. By dividing the service area into independent sectors or adaptively nulling interferers (so-called “space time adaptive processing”), MAI from other users that are directionally resolvable may be substantially reduced. U.S. Pat. Nos. 6,101,399, 6,078,823, and 5,953,325 are examples of this technique. Yet another technique utilizes complex, non-linear algorithms in the receiver to concurrently estimate the signals from a multitude of users, as shown in U.S. Pat. Nos. 6,081,516, 6,014,373, and 5,956,333. Termed multi-user detection (MUD), such approaches require extensive computational resources at the receiver and, as such, are suitable for use on the uplink (at the BS) but not on the downlink (at the mobile).
As mentioned earlier, the use of repeaters also has been introduced in the field of spread spectrum, wireless communication. Conventional repeaters appear to fall into one of two categories: channel conversion and multipath simulation. A channel-conversion repeater takes the signals received at the repeater and converts them to an alternate radio resource, such as another frequency band or another channelization code. The industry standard organization for next generation, i.e. third generation (3G), CDMA systems has included one implementation of such a repeater in its standard. Termed Opportunity Driven Multiple Access (ODMA), that configuration is discussed in the Third Generation Partnership Project (3GPP) Technical Report 25.924 version 1.0.0. A number of patents, such as U.S. Pat. Nos. 5,887,261 and 6,141,533, also relate to the use of repeaters. Specifically, U.S. Pat. No. 5,887,261 describes a non-selective channel converting repeater, and U.S. Pat. No. 6,141,533 describes a repeater design that converts and relays selected traffic and control channels. This selective design may be viewed as having nearly the functionality of a BS except that the link to the network infrastructure is carried on typical network voice and traffic channels back to an actual BS. In contrast, a multipath simulating repeater generally takes the entire received RF signal, introduces a delay on the order of several microseconds, and re-transmits the signal. The intent is to preserve any signal diversity as seen by the repeater in a manner that the link termination may exploit with a RAKE receiver. U.S. Pat. Nos. 5,930,293, 5,652,765, 5,991,345, and 6,035,218 are examples.
Additionally, U.S. Pat. Nos. 5,835,848, 5,812,933, and 6,108,364 focus on the necessity for substantive isolation between the transmit and receive subsystems for repeaters that do not provide frequency conversion. Finally, there are patents, such as U.S. Pat. Nos. 5,936,754, 5,867,485, and 5,809,422, that propose remote emitters linked to the BS via means other than an in-band radio frequency (RF) transmission to support both the uplink and downlink.